The present invention is concerned with a method for inducing female sterilization and to compositions for use in such method.
Broadly stated, the method of the invention involves blocking the fallopian tubes or oviducts by using radiopaque additives in conjunction with a composition which causes inflammation of the inside or mucous lining of the tubes so as to generate scar tissue sufficient to block the tubes. The composition itself is biodegradable and leaves no residue, the oviducts being closed solely by the scar tissue which is subsequently formed. The ratiopaque additive should also be rapidly cleared from the oviducts and the body.
The invention contemplates using methyl cyanoacrylate (MCA) as the composition for effecting the desired inflammation and formation of scar tissue in the tubes. Cyanoacrylates are known to be adhesives and certain cyanoacrylates, e.g. isobutyl cyanoacrylate (IBCA) have been used for therapeutic embolization to obliterate blood vessels. See, for example, "Modification of Cyanoacrylate for Therapeutic Embolization: Preliminary Experience" by Cromwell et al, AJR: 132, May 1979, pages 799-801. Cromwell et al indicate that the cyanoacrylates suffer from two main disadvantages when used as tissue adhesives i.e they polymerize so rapidly on contact with ionic materials, e.g. blood, that a physician only has 1-2 seconds to make the needed injection; and they are not radiopaque. Cromwell et al have shown that the IBCA polymerization or set-up rate can be slowed and also that the formulation can be made suitably radiopaque for therapeutic embolism by adding iophendylate, i.e ethyl-10-(iodophenyl) undecanoate, to the cyanoacrylate.
Freeny et al in a paper entitled "Long-Term Radiographic-Pathologic Follow-Up of Patients Treated With Visceral Transcatheter Occlusion Using Isobutyl-2-Cyanoacrylate (Bucrylate)", Diagnostic Radiology, July 1979, pages 51-60, have described additional work regarding the use of IBCA for therapeutic thrombotic occulsion.
The purpose of the work referred to in the Cromwell et al and Freeny et al papers noted above is fundamentally different from that of the present invention. More specifically, the purpose of using IBCA according to the aforementioned papers is to occlude blood vessels, while causing as little as possible inflammatory response of the blood vessel wall and surrounding tissues and organs. This is called "transcatheter occlusive therapy", the blood vessels being occluded with blood clot (thrombus) plus polymerized IBCA, which does not degrade significantly in the body. This sort of therapy can be used to occlude hemorrhaging blood vessels, to identify the extent of tumor growth, to block blood flow to tumors and to treat various blood vessel malformations. In all of these cases, the occlusion agent is polymerized IBCA which remains in place and does not degrade away.
In contrast, the MCA of the present invention functions by inducing a significant inflammatory response on the inside lining of the oviducts, such that dense fibrous scar tissue is deposited across the oviduct lumen. At the same time, the MCA polymerizes to form a polymer which degrades and disappears from the site. Thus, the oviduct becomes occluded by natural scar tissue formed as a result of the inflammation caused by the MCA with no residues of the resultant MCA polymer remaining. It will thus be seen that the MCA in the present case functions in a completely different way from the IBCA used for transcatheter occlusive therapy according to Cromwell et al and Freeny et al.
The possibility of using MCA to block the fallopian tubes for sterilization purposes has previously been described. See, for example, paper entitled "The Effect of Methyl Cyanoacrylate Tissue Adhesive on the Human Fallopian Tube and Endometrium" by Stevenson et al, The Journal of Obstetrics and Gynaecology of the British Commonwealth, Nov. 1972, Vol. 79, pp. 1028-1039. This use of MCA is also disclosed by: Neuwirth et al, Am. J. Obstet. Gynecol., Vol. 129, No. 3, pp. 348-349, Oct. 1, 1977; Neuwirth et al, Contraception, December 1977, Vol. 16, No. 6, pp. 581-589; Corfman et al, Science, Vol. 148, pp. 1348-1350, June 1965; and Neuwirth et al, Am. J. Obstet. Gynecol., Vol. 136, No. 7, pp. 951-956, Apr. 1, 1980.
While the abovementioned publications disclose the use of MCA for female sterilization, they do not disclose the unique combination of the present invention, i.e. the use of MCA together with a low viscosity, water-immiscible radiopaque compound which is miscible with the MCA and which may also serve to lengthen the shelf-life of the MCA, while at the same time conferring the essential X-radiopacity to the mixture. Advantageously the selected radiopaque additive is one which tends to retard the cyanoacrylate set-up time, e.g. the material known as "Pantopaque". This can be an advantage in avoiding premature set-up in the uterus and blockage of the UTJ (uteral-tubal junction) which would prevent entry of the mixture into the tubes. Furthermore, once the composition enters the oviducts, the slower set-up rate can permit better filling of the tubes, both in cross-section and lengthwise. The radiopaque additive used according to the invention may or may not incite an acute inflammatory response (i.e., it may or may not be a sclerosing agent, as is the MCA). However it should be cleared from the body reasonably quickly and to an extent such that there are no undesirable long-term effects. The radiopaque nature of the additive is desirable to aid in visualizing whether or not the tubal blockage is bilateral and otherwise adequate. It may also be useful in training paramedical personnel and has the potential for raising the success rate for bilateral occlusion on one visit.
A preferred radiopaque additive is ethyl-10-(iodophenyl) undecanoate which is commercially available as the aforementioned "Pantopaque" (Lafayette Pharmacal, Inc.). This compound has the formula: ##STR1## Other iodinated organic compounds may also be used as the ratiopaque additive e.g. ethiodized ethyl esters of the fatty acids of poppyseed oil (available as "Ethiodol" from Savage Laboratories) or aqueous organic iodides reacted to make them water-immiscible. Variations of these compounds are also possible such as more highly iodinated analogues of "Pantopaque" or the ethiodation esters of the fatty acids of vegetable or flower oils, fish oils, etc. Essentially any water-immiscible organic compound containing aromatic rings or unsaturated groups may be halogenated (e.g., iodinated, brominated, etc.) to yield a cyanoacrylate-miscible, radiopaque stabilizing additive suitable for use herein.
It is also possible to use radiopaque additives other than organic halides. Examples of such additives include: tantalum powder, silica powder, barium sulfate powder, Teflon powder, polyvinyl chloride (PVC) powder, calcium carbonate powder, silver powder, silver compounds and bismuth compounds. In this connection, attention is called to U.S. Pat. No. 3,896,077 which describes adhesive paste compositions comprising alpha-cyanoacrylic acid esters, including MCA, and certain insoluble inorganic fillers, e.g. calcium carbonate. Some of the MCA-paste compositions described in U.S. Pat. No. 3,896,077 may be used for present purposes although it is preferred to use "Pantopaque" or equivalent additive.
As a further modification the radiopaque substance may be attached to the cyanoacrylate itself, e.g. as iodomethylcyanoacrylate of the formula: ##STR2## or as iodophenylcyanoacrylate of the formula: ##STR3## In certain situations this sort of modification may have the advantage of enhanced polymerization rate and set-up time for the liquid mixture when compared with mixtures of, for example, MCA and Pantopaque.
It will be appreciated from the foregoing that the present invention contemplates the use of a liquid mixture for tubal instillation which will induce female sterilization by bilateral blockage of both oviducts, resulting from natural fibrous tissue deposition within the tubes. The liquid mixture is further characterized by the following properties: it sets up or solidifies rapidly although in a desirably controlled fashion, by polymerization, so to avoid spillage into the peritoneum; it is radiopaque in order to verify bilateral entrance; it induces a significant local inflammatory ("toxic") response within the tubes; it disappears by biodegradation and diffusion of breakdown products and radiopaque additives as fibrous tissue is deposited in its place; and it does not cause any other undesirable response within the body.
In some cases the radiopaque additive may tend to undesirably slow the setting of the instillation mixture. In that event it may be desirable to include in the mixture another additive which is intended to speed up the rate of solidification or polymerization of the liquid mixture in vivo, i.e. after it is instilled into the oviducts, in order to avoid spillage into the peritoneal cavity. For this purpose, a faster-curing cyanoacrylate (e.g. IBCA) may be mixed with the MCA and radiopaque additive to provide a liquid water-free mixture for use according to the invention. However, since MCA is the most active of the alkyl cyanoacrylates in eliciting an inflammatory response and subsequent fibrous tissue deposition, and since poly-MCA is the only poly-cyanoacrylate which biodegrades at a significant rate, any modification of the mixture to include IBCA or other additives needs to be clearfully designed (e.g. to avoid segments of pure poly IBCA in the cured polymer). Thus, it is anticipated that at most up to ca 20% (vol.), and preferably not more than 10%, of IBCA may be mixed with MCA to achieve the optimum behavior of rapid curing and reasonably rapid polycyanoacrylate biodegradation and disappearance accompanied by scar tissue deposition.
Other essential additives to the cyanacrylate and radiopaque substance formulation include polymerization inhibitors to enhance the shelf life of the formulation and to inhibit premature curing before the system sets up in the oviduct. Two types of such inhibitors should be used: (1) acids such as SO.sub.2, p-toluene sulfonic acid, formic acid, acetic acid, etc. and (2) free radical traps such as hydroquinone, hindered phenols and their derivatives. The acid inhibitors will usually be used in the amount of from 0 to 5% by volume (based on the MCA), preferably from 0.01 to 3%. The amount of free radical stabilizers will usually be in the range of 0 to 5% by weight of MCA, preferably 0.01 to 1% by weight.
Ideally, the components making up the liquid water-free mixture of the invention are totally miscible with each other to give a single phase composition. The presence of multiphases may cause instillation problems, e.g. plugging of the injector used to insert the mixture. Multiphase compositions can be used but extra precaution must be taken to avoid such plugging.
As a further modification of the invention it is also contemplated that two separate solutions may be sequentially or simultaneously but separately instilled rather than using a single mixture. For example, an aqueous radiopaque solution and liquid MCA may be injected separately but more or less simultaneously to the desired body site. One possible sequence is as follows: (a) instill the aqueous or organic radiopaque additive system, (b) take an X-ray, (c) instill the MCA, and (d) take another X-ray to verify tubal blockages by the movement of the radiopaque fluid in the oviducts. This could be important in permitting use of aqueous radiopaque additives (which would normally cure the MCA if mixed with it) in a sequence with the non-aqueous MCA instillation.
As an illustration of a composition suitable for present purposes there may be mentioned a blend of 25% by volume of Pantopaque dissolved in MCA. Such a mixture was prepared by blending the Pantopaque in the MCA in the absence of moisture. The mixture (MCA/P) was stored in the dark at room temperature (20.degree.-25.degree. C.). It retained its original low viscosity, free-flowing liquid condition even after storage for 10 months. Samples of MCA/P (25%) mixtures were also instilled into sections of freshly excised human oviducts. X-rays showed the tubes were filled with the MCA-Pantopaque mixture.
The amount of radiopaque additive used according to the invention can be varied depending on the nature of the additive itself and other factors. With Pantopaque as the additive, optimum results appear to be obtained with a mixture as described above comprising about 25% by volume of additive, based on the total volume of additive and MCA. However, it will be appreciated that the amount of Pantapaque and/or other additive can be varied over a relatively wide range to give the desired degree of radiopaqueness and set-up time.